Heretofore, in induction hardening of a shaft member having multiple steps, a method has been performed in which hardening is performed by heating using an annular heating coil corresponding to each step or each set of steps of the shaft, followed by cooling. However, by the above conventional method, there have been problems in that the cost is increased due the complication thereof, and root portions of the steps are not easily heated up.
Accordingly, as an induction heating coil which solves the above problems, a heating coil has been disclosed in Patent Document 1.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 11-162626